1. Field of the Invention
The present invention relates to an optically active isosorbide derivative and an optically active isomannide derivative which each have a photosensitive property, respective production methods thereof, a photo-reactive chiral agent which causes a change in a liquid crystal structure, a liquid crystal composition comprising the chiral agent, a liquid crystal color filter, an optical film and recording medium and a method for changing or fixing the helical structure of the liquid crystal.
2. Description of the Related Art
In recent years, a liquid crystal material has attracted people's attention; for example, a cholesteric liquid crystal compound which has a helical structure and exhibits a variety of selectively reflected colors caused by a twisting power (twisting angle) based on the helical structure is excellent in a selective reflection property or color purity of selectively reflected light, thereby being widely used in an optical film, a liquid crystal color filter, a recording medium and the like.
A present situation thereof will be explained below taking, for example, a color filter.
The color filter for use in, for example, a color liquid crystal display is ordinarily constituted by respective pixels of red (R), green (G) and blue (B), and a black matrix formed in a space between any two pixels for improving a display contrast.
As for such color filters, a color filter in which a pigment is dispersed in a resin or the resin is dyed with a coloring agent is prevailing. Further, as for production methods thereof, a production method in which a colored resist layer is formed by applying a colored resin solution on a glass substrate by spin coating or the like and, then, patterning is performed on the thus-formed colored resist layer by a photolithographic technique to form a color filter pixel or another production method in which a colored pixel is directly printed on the substrate has ordinarily been adopted.
However, for example, in the production method by the printing technique, there has been a drawback that resolution of the pixel is low and such low resolution makes it difficult to respond to formation of a high-definition image pattern, while in the production method by such spin coating technique, there has been a drawback that waste of a material is large and also large coating unevenness is generated when the substrate having a large area is coated. Further, according to a production method by an electrodeposition technique, there has been a drawback that, although the color filter in which the resolution is comparatively high and unevenness of a colored layer is small can be obtained, production steps are complicated and also solution control is difficult.
Under these circumstances, as for the production methods of the color filter, a production method in which the waste of the material is small and a high-quality color filter can be produced in an efficient and convenient manner is required.
On the other hand, as for properties of the color filter, high transmittance and high color purity are required. In recent years, various improvements have been attempted for responding to such requirements, for example, by optimizing a type of the coloring agent or a resin dyed with the coloring agent in a method using a coloring agent and by employing a finely dispersed pigment in a method using a pigment. However, requirements for transmittance and color purity of the color filter in a recent liquid crystal display (LCD) panel are extremely high and, particularly in the color filter for use in a reflection type LCD, it is difficult to simultaneously satisfy white representation of paper white, contrast and color reproducibility and, further, since the color filter which is produced by dying the resin by the coloring agent or dispersing the pigment therein by a conventional production method is of light-absorption type, an improvement of color purity by further enhancing transmittance has nearly reached the limit.
Against such situation as described above, the color filter of a polarization utilization type comprising a cholesteric liquid crystal as a main component has attracted people's attention. This color filter of the polarization utilization type performs an image display by reflecting a given quantity of light and transmitting the remaining quantity of light, thereby having inherently high utilization efficiency of light and also remarkable properties in the transmittance and color purity compared with the color filter of the light-absorption type. On the other hand, as for production methods, from the standpoint of capability of obtaining uniform thickness, a method of forming a film on a substrate by utilizing the spin coating technique or the like has ordinarily been adopted; however, since the waste of the material was large, this method was disadvantageous from the standpoint of cost.
For the purpose of solving the above-described problems, allowing the uniformity of the color purity or the like of the color filter film to be secured and realizing a reduction of a number of production steps, a method using a photo-reactive chiral compound is effective. This method utilizes a theory that, when light having a wavelength reactive to the photo-reactive chiral compound is patternwise irradiated on a liquid crystal composition containing the photo-reactive chiral compound, a reaction advances in the chiral compound in accordance with an intensity of irradiation energy to change a helical pitch (helical twisting angle) of the crystal compound whereupon, only by patternwise exposure having different light quantities, a selectively reflected color is formed per pixel. In other words, this method has a merit in frequency of patterning at the time of forming the color filter such that it can be completed by performing only one-time mask exposure using a mask having different transmission light quantities.
Therefore, after the patterning is performed by irradiating light imagewise, a film which functions as the color filter can be formed by fixing the cholesteric crystal compound which has been subjected to patterning. This technique can be utilized also for an optical film, image recording and the like.
Particularly, in a case in which the color filter is formed by one-time mask exposure or other appropriate cases, it is desired that three primary colors, that is, B (blue), G (green) and R (red), can be formed with favorable color purity by one-time exposure. However, when a helical twisting change ratio is small, sufficient color purity can not be obtained. Therefore, in view of allowing three primary colors of high color purity to be displayed by one-time exposure, as a photo-reactive chiral compound on a practical point of view, it is necessary to use a chiral compound (chiral agent) having a large helical twisting change ratio which can substantially change the twisting power of the helical structure of the crystal compound. Namely, by using the chiral compound having a large helical twisting change ratio, a range of hues which is selectively reflected in accordance with a light quantity change can be expanded.
As examples of such chiral compounds, the present inventor disclose a photo-reactive chiral agent, having a isosorbide skeleton which has been esterified by a cinnamic acid derivative, described in Japanese Patent Application Laid-Open (JP-A) Nos. 2002-80851, 2002-179682, 2002-179681 and 2002-338575. Further, a photo-reactive chiral agent of benzylidene menthone type is disclosed in WO 00/34808.
On the other hand, a light source for use in the mask exposure is ordinarily a mercury lamp of super high pressure type having a emission line at 365 nm whereupon it is desirable that, for the purpose of allowing sensitivity at the time of the mask exposure to be high, that is, a reaction of the chiral compound to be faster, a molar absorption coefficient of the chiral agent is large in this wavelength region.
However, the chiral agent disclosed above had a drawback that, since the molar absorption coefficient thereof at 365 nm is small, the sensitivity at the time of the mask exposure is low, or a cis form to be generated by performing photo-isomerization is lack in thermal stability.
Further, although the present inventor also discloses a photo-reactive chiral agent having an isomannide skeleton which has been esterified by a cinnamic acid derivative in JP-A No. 2002-80478 as a chiral agent, the chiral agent also had a drawback that the molar absorption coefficient at 365 nm was small and the sensitivity at the time of the mask exposure was low.
As described above, it is a present situation that a photo-reactive chiral agent which is imparted with a photo-reactive property capable of changing an orientation structure such as a helical pitch (helical twisting power, helical twisting angle) of the liquid crystal in accordance with an irradiated light quantity and, for example, in case of a cholesteric liquid crystal phase comprising a nematic liquid crystal compound, and can substantially change the helical pitch (helical twisting power) thereof such that it has a wide range of wavelength capable of performing selective reflection, thereby allowing a variety of selective reflection to be exhibited and, particularly, allowing 3 primary colors (B, G, R) to be displayed in high color purity has not been provided.